Project Summary/Abstract Cognitive skills are the crucial abilities required to manage money, maintain employment, and live independently. Long-term cognitive impairment (LTCI) is a disabling loss of these skills that can persist for months to years. LTCI frequently occurs after primary brain injury (e.g., traumatic brain injury, hypoxia), but older LTCI research has not characterized primary brain injury using NIH Common Data Elements in Imaging, the contributions of polytrauma, and the time-course of the critical illness, including secondary brain injury (i.e., delirium). In our recent large study of ICU patients without primary brain injury, over 50% of patients had LTCI and nearly 50% were newly unemployed at one-year post-discharge. In-hospital delirium was the major independent risk factor for LTCI. Surprisingly, this delirium-related LTCI was similar to the LTCI seen in past studies after moderate traumatic brain injury. Thus, both primary and secondary brain injury are associated with LTCI, yet they have not been studied together. There is an unmet need to define the independent risks of primary brain injury and delirium in LTCI. The trauma ICU patient is at combined risk for primary brain and/or multisystem injuries, secondary brain injury, and critical illness; these critically injured patients are the unique population to address this knowledge gap. Therefore, our FIRST HYPOTHESIS is that delirium duration is an independent risk for the severity of LTCI, controlling for confounders of co-morbidities, socioeconomic status, pre-injury employment, primary brain injury, polytrauma, and critical illness. AIM 1 will address this hypothesis by defining the independent risks of primary and secondary brain injury on the severity of LTCI among 900 trauma ICU subjects. But, LTCI's real-world impact on employment has not been explained or adjusted for the above confounders and social factors. Accordingly, our SECOND HYPOTHESIS is that LTCI severity is an independent risk for lower level of employment, adjusting for similar confounders. AIM 2 will delineate the independent risk of LTCI severity on employment among trauma ICU survivors. Lastly, LTCI pathogenesis may be related to persistent inflammation. So, our THIRD HYPOTHESIS is that hospital discharge biomarkers of persistent inflammation will be independent risks for LTCI severity, adjusting for similar confounders. AIM 3 will explore the mechanistic role of plasma inflammatory biomarkers on LTCI severity among trauma ICU survivors.